1. Field of the Invention
The present invention relates to an intake system for an internal combustion engine, more particularly to an intake system provided with a chamber of a predetermined volume located adjacent to an engine intake pipe and connected at one side to an intake passageway upstream of an intake manifold and downstream of an air cleaner so as to make effective use of the dynamic action of the intake air.
2. Background of the Invention
It is well known that, in an internal combustion engine, one can increase volumetric efficiency and achieve improved engine output and torque by making use of the so-called dynamic intake effect. The dynamic intake effect is achieved at the engine rotational speed, or whole multiples thereof, corresponding to the natural frequency of the intake pipe. Therefore, one can design an engine so as to achieve the dynamic intake effect at a certain rotational speed by selecting a suitable length of the intake pipe.
Obviously, it is desirable to obtain this dynamic intake effect at engine rotational speeds other than that corresponding to the fundamental natural frequency of the intake pipe or a multiple thereof. Toward this end, it has been proposed to provide an intake system equipped with a chamber of a predetermined volume adjacent to the engine intake pipe. The chamber is connected to the intake pipe by way of a control valve which is opened or closed in accordance with the engine operating conditions, in particular, the engine rotational speed. (See Japanese Unexamined Patent Publication (Kokai) No. 55-87821.)
With this chamber, it is possible to change the effective intake pipe length, and thus the natural frequency of the intake pipe, by just opening or closing the control valve. Thus, it is possible to cause different engine rotational speeds to produce V peaks in rotational speed-volumetric efficiency (.eta.V) curves. During engine operation, the control valve is opened or closed in accordance with the engine rotational speed so as to select the volumetric efficiency (nV) curve resulting in the higher volumetric efficiency. This enables increased torque to be obtained at every range of engine rotational speed.
This prior art arrangement suffers, however, from the drawback of increased noise during induction of intake air. This is principally due to the fact that the point where the air cleaner is connected to the intake pipe must act as an "open end" in the dynamic intake effect when the control valve is closed. For this reason, the air cleaner should have a nose of a shortened length. This shortened nose causes increased noise when intake air flows into the air cleaner.